The present invention relates to a regenerative braking control system for an electric vehicle driven by an electric power supply, namely a battery. More specifically, the present invention relates to a regenerative braking control system for electric vehicle which is capable of individually controlling the charging current for recharging the battery and the braking force applied by the brakes.
The present invention also relates to a controller for an electric vehicle driven by an electric motor. More specifically, the present invention relates to a controller for an electric vehicle which is capable of securing satisfactory controllability even if a portion of the electric system for controlling the driving of the drive motor malfunctions during a running operation.
Regenerative braking is used widely as an energy saving means for an electric vehicle employing a DC motor as its driving force. Regenerative braking is achieved by interrupting the power supply to the DC motor, converting the kinetic energy of the DC motor into electric energy, and utilizing this electric energy to recharge the power supply.
FIG. 5 is a block diagram illustrating a portion of the motor control system for an electric vehicle. FIG. 6 is a timing diagram which illustrates the procedure for controlling the regenerative braking process.
Referring to FIG. 5, driving coils U, V, and W are wound on a stator 37, and a rotor shaft 19 is mounted with a rotor 51 and a magnet rotor 48 for rotation within the central portion of the stator 37. Hall-effect devices UH, VH, and WH are arranged around the magnet rotor 48 for determining, in a non-contactual manner, the angular position of the rotor 51. Detection signals produced by the Hall-effect devices are fed to an angular position detecting device 46. The angular position detecting device 46 determines the angular position of the rotor 51 based on the detection signals and produces an angular position signal which is fed to a commutation/rectification control device 45.
The commutation/rectification control device 45 includes a running mode commutation control device 45a which operates during the normal running state, a regenerative mode rectification control device 45b which operates during a regenerative state, and a switching circuit 45c for selecting either the running mode commutation control device 45a or the regenerative mode rectification control device 45b.
The driving coils U, V, and W are connected to a commutating/rectifying device 90. This commutating/rectifying device 90 includes a switching unit 90a which includes transistors and diodes in combination and a pre-driving unit 90b. The switching unit 90a controls the power supplied from a battery BA to the driving coils U, V, and W. This switching unit 90a also acts as a path for feeding the recharging power from the driving coils to the battery BA.
During a normal running state, the switching circuit 45c selects the running mode commutation control device 45a so that the commutation/rectification control device 45 operates properly during the running mode.
The running mode commutation control device 45a switches the transistors of the switching unit 90a ON and OFF so that the power being supplied from the battery BA to the driving coils U, V, and W is carried out according to a predetermined timing scheme.
Consequently, a DC drive motor M is driven in a rotational manner by the power supply thereto from the battery BA such that the electric vehicle is driven.
On the other hand, in a regenerative braking mode, the duty factor of a pulse signal for controlling the power supplied to the drive motor M (driving duty factor) is reduced to zero. Upon the detection of the reduction of the driving duty factor to zero, a braking detecting device 79 produces a braking detection signal which is fed to the switching circuit 45c. The switching circuit 45c then selects the regenerative mode rectification control device 45b.
The regenerative mode rectification control device 45b switches the transistors ON and OFF so that regenerative power is produced by the drive motor M and consumed by the commutating/rectifying device 90 and the driving coils U, V, and W for braking.
In the regenerative braking mode, a three phase AC voltage as shown in FIG. 6(a) is produced by the driving coils U, V, and W. During this state of operation, the regenerative mode rectification control device 45b feeds a pulse signal to the transistors UTr.sub.1, VTr.sub.1, and WTr.sub.1 so that these transistors are turned OFF. Moreover, the regenerative mode rectification control device 45b supplies a pulse signal, as shown in FIG. 6(b), to the transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 so as to turn these transistors OFF and ON periodically and simultaneously.
When the transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 are turned OFF, currents induced in the driving coils tend to remain, and hence, a high voltage remains across each coil which can be utilized in recharging the battery BA.
Since the magnitude of the regenerative braking force is proportional to the energy consumed by the transistors, diodes, and driving coils while the transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 are switched ON, the magnitude of the regenerative braking force is proportional to the pulsewidth of the pulse signal. Accordingly, the pulsewidth is increased when a large braking force is desired, and the pulsewidth is decreased or diminished, as shown in FIG. 6(c), when a small braking force is desired.
The prior art device which utilizes this pulsewidth to control the braking force. However, such a method has encountered many problems in the actual regulation of the pulsewidth of the pulse signal. Since the induced current for recharging the battery BA is dependent upon the electromotive force of each coil when the transistors are turned OFF, the amount of charging energy is substantially constant regardless of the pulsewidth of the pulse signal. The only exception to this situation is when the pulsewidth is small and the electromotive force is in a transient state. Accordingly, the braking force and the recharging energy in the prior art devices could not be controlled individually.
Since the prior art devices were not able to control the braking force and the recharging energy individually, the prior art devices found it impossible to carry out a control operation, for example, which decreases the recharging energy when the battery is fully charged and increases the recharging energy when the battery is not fully charged notwithstanding the actual priority to be given to the controlling of the braking force.
More specifically, the prior art devices place the braking force as the highest priority and thus ignored the controlling of the recharging energy. Consequently, by ignoring the controlling of the recharging energy, either the battery became overcharged by regenerative braking when the battery was already basically overcharged or the battery could not be readily recharged to its full capacity if the battery was not already fully charged prior to the regenerative process.
Therefore, one embodiment of the present invention provides a regenerative braking control system for an electric vehicle which is capable of individually controlling the braking force and the recharging energy during a regenerative braking mode.
FIG. 34 is a block diagram illustrating a portion of an electric system for controlling the driving of the drive motor of an electric vehicle. Driving coils U, V, and W are wound on a stator 37 of a drive motor M. A rotor 51 and a magnet rotor 48 are supported for rotation in a central portion of the stator 47. Hall-effect position sensors UH, VH, and WH determine, in a non-contactual manner, the angular position of the rotor 51. These position sensors provide position detection signals to a controller 10.
A driver 90 includes a switching circuit 90a which includes transistors and diodes and a pre-driving unit 90b. The driver 90 controls power supplied from a battery BA to the driving coils U, V, and W. Moreover, the driver 90 controls the recharging of the battery BA by the energy generated in the driving coils.
A motor temperature sensor 21 detects the temperature of the drive motor M and produces a temperature signal TM representing the temperature of the drive motor and feeds this temperature signal to the controller 10. An accelerator position sensor 22 detects the position of the accelerator and produces an accelerator position signal TH which represents the actual position of the accelerator and feeds this signal to the controller 10. The controller 10 determines the rotor position based on the position signals received from the position sensors.
FIG. 35 illustrates a table showing the detection signals provided by the position sensors and the corresponding angular positions of the rotor. For example, when the Hall-effect position sensors UH, VH, and WH detect an N-pole, an S-pole, and an S-pole, respectively, the rotor is at an angular position as illustrated by number 1 in FIG. 35.
The controller 10 determines, on the basis of the accelerator position signal TH, whether the vehicle is in a driving mode (the vehicle is being driven by the drive motor) or whether the vehicle is in a braking mode (when the vehicle is being braked). If the vehicle is in the driving mode, the controller 10 produces output signals to be fed to the transistors of the switching unit 90a as illustrated in FIG. 36.
These output signals are produced according to the angular position of the rotor 51. Moreover, the controller 10 controls the duty factor of a motor driving signal supplied to the drive motor M (driving duty factor) according to the accelerator position signal TH. Consequently, the magnitude of the power corresponding to the accelerator position is supplied from the battery BA to the drive motor M when the electric vehicle is in the driving mode.
During the braking mode, an electric brake is applied. FIGS. 6(a)-6(c) illustrate timing charts of the control mode for electrical braking. When power supplied to the drive motor M is terminated, three phase voltage, as shown in FIG. 6(a) is generated in coils U, V, and W, respectively. During this electrical braking mode, the transistors UTr.sub.1, VTr.sub.1, and WTr.sub.1 are turned OFF. Also, a pulse signal, as illustrated in FIG. 6(b), is applied to transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 to turn OFF and ON these transistors periodically and simultaneously. Consequently, the electromotive force generated by the coils is consumed as heat by the coils, transistors, and the diodes when the transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 are switched ON. This allows the drive motor M to be braked.
When these transistors are switched OFF, the currents induced in the coils tend to remain. This in turn maintains a high voltage across the terminals of each coil. If the voltage across the terminals of each coil is higher than the supply voltage of the battery BA, the induced currents flow toward the battery BA to recharge this battery.
Since the braking force is proportional to the energy consumed by the transistors and diodes while the transistors UTr.sub.2, VTr.sub.2, and WTr.sub.2 are switched ON, the braking force is proportional to the duty factor of the pulse signal (braking duty factor). Accordingly, the braking duty factor is increased (the pulsewidth is increased) when a high braking force is necessary. Moreover, the braking duty factor is decreased (the pulsewidth is decreased) when a low braking force is necessary.
The prior art devices which utilize the system described above are also provided with a second controller for turning OFF all of the transistors of the driver 90 to stop the power from being supplied to the drive motor M, thereby preventing adverse effects upon the components of the electrical system when all of the position sensors produce the same position detection signals due to a malfunction or when the control of the power supplied to the drive motor becomes impossible. This hindrance of the controlling of the power supplied to the drive motor M may occur due to a malfunction of the accelerator position sensor or when the temperature of the drive motor increases excessively.
If all of the transistors of the driver 90 are turned OFF by the second controller when a portion of the electric system malfunctions, the driving wheels of the electric vehicle cannot be properly braked by using regenerative braking. Thus, the electric vehicle must be braked by using a mechanical braking system in order to stop the vehicle properly. In other words, the electric vehicle cannot decelerate in a satisfactory manner. Therefore, if all of the transistors of the driver 90 are turned OFF, the control of the electric vehicle according to the operations of the throttle, becomes impossible.
Accordingly, one embodiment of the present invention provides a controller for an electric vehicle which is capable of satisfactorily controlling the electric system of an electric vehicle even if a portion of the electric system for controlling the drive motor of the electric vehicle malfunctions.